The Yin and Yang: Swallowtail butterflies

Review: Evolution Basics


  • Evolution:


  • Population:

    • group of individuals of the same species, occupying the same time and space, with the potential of interbreeding

  • Species:

    • group of living organisms consisting of similar individuals capable of exchanging genes or interbreeding successfully


  • Evolution by Natural Selection:

    • organisms with heritable traits that favor survival and reproduction will tend to leave more offspring than their peers, causing the traits to increase in frequency over generations

Brown et al. 2007: 6 genetically distinct lineages of giraffe

Evolution by Natural Selection: Darwin and others



  • A few things need to be true…


  • Individuals in a population are not identical
  • Some variation among individuals is heritable
  • Individuals sometimes die before reproducing
  • Different ancestors leave different #’s of descendants



  • If enough change results in reproductive isolation between populations, new species can evolve

What is Generational Time? Why does it matter?

Generation time determines the rate (speed) of evolution

Species are so specialized, they are absent almost everywhere

How does this related to the dualism between ecology and evolution?



















How many species of bees do you think there are in the USA?

The ‘Tree of Life’ evolved over geologic time periods

Why does this matter for Ecology?




  • Survival of the fittest is tied to organisms interacting with their environment (living & non-living)


  • This term is a little misleading, should read:
  • Survival of the better designed for an immediate, local environment
  • survived death
  • reproduced successfully


  • The components and themes of ecology matter a lot!
  • environments are often not stable for very long

Ecological forces drive evolution




  • Some traits of living things are ‘conserved’
    • not easily modified


  • However,we often seem lots of variation within a species


  • Traits of a species often vary over geographic ranges
    • why?

’Ohi’a lehua tree on Hawaiian Islands

Within species variation can occur at short distances

Evolution also driven by species interactions



  • Selection forces: pressures on an trait by natural selection driving evolution of a population



  • Steam guppies in Trinidad are separated by waterfalls
    • isolated populations
    • tons of different traits across guppy populations


  • What selection forces could be driving these changes?

Predation, sex and flamboyance in guppies

When species interact, co-evolution can occur

Co-evolution of orchid bee and ochid flowers

This Yin and Yang is key for life on land

Ecologically driven speciation



  • Divergent selection between different environments leads to the creation of reproductive barriers
    • driven by difference in environment
    • driven by interaction with other species



  • Populations become isolated, then selection drives change


  • Eventually may lead to evolution of new species

Adaptive Radiation: Rapid speciation with sudden change

We view the past & present of evolution with phylogenetic trees

Take Home Messages

  • There is a reciprocal relationship between evolution and ecology
    • swallowtail catepillars


  • Ecological processes enact strong selection pressures on species
    • guppy


  • Ecology plays a specific role in a tenant of natural selection: reproductive isolation
    • giraffe


  • Patterns in ecological processes have driven evolution over very long periods of time…
    • flowering plants and insects